3 years ago

can time be ever negative?

To understand this one needs to know what time actually is. Our understanding is related to `seconds,minutes, hours, days..’. This is a `measure’ of time-counting. One must relate time to some physical quantity. It is difficult to explain such a physical quantity but one might say time is related to a physical quantity which always increases.
Negative time has been thought of by some people. It refers to `before the beginning of the universe’. This is largely hypothethical and one need not get into such discussions.
For us it is just about enough to assume t=0 as the beginning of time and the forward progression of time.

The reply above is a good summary. But, I will add that for some simple physics questions, if you have a graph with time as one of the axes, then you can get time as a negative quantity (although the time won't really be negative, but will appear negative relative to the moment you took as t = 0 at the origin.)
For example, if you use the equation
\[s=ut + (1/2)at^2\]
Then you can get a negative value for t, because
\[t = \pm \sqrt{2(s-ut)/a}\]
(the square-root has two answers, positive and negative)
However, usually you ignore the negative answer, but it is good to include it in an answer, to show you understand your maths, and then state that you will ignore it because it will not be in the time period of your question.

the concept of negative time is very simple when you use it as frame of reference. For example, if you are at Delhi at 0700hrs, then at 1000hrs if you are at kolkata, at 1500hrs in chennai. if you take 1000hrs as reference time frame T, then you were at Delhi at T-3hrs ! But there is no such negative time in reality